CASE in WHERE in mysql -

this question has answer here:

• case in clause in mysql 1 answer

the question simple title says,but here 1 logic. here code

create table `inf_brand_images` ( `id` bigint(99) not null auto_increment, `brand` varchar(255) not null, `thumb` text not null, `is_active` int(2) not null default '1', `cmp_brand` varchar(1024) not null, primary key (`id`) ) engine=myisam auto_increment=6458 default charset=latin1 

here data in table

id | brand  | thumb  |is_active| cmp_brand 1  | nike   | a.png  | 1       |  2  | dunhill| b.png  | 1       | 3  | nike   | c.png  | 1       | 123_nike 4  | nike   | d.png  | 1       | 789_nike 

cmp_brand prefixed ids 123_ , 789_ in case. if search nike, have 2 parameters,one nike , other id_nike.where id may 123 or 456 or other.

what want is

if cmp_brand '' compare brand else compare brand , cmp_brand. 

here tried

select thumb  inf_brand_images  is_active=1  ,  case when cmp_brand = '' brand='$brandname'  else cmp_brand='$id_$brandname' end 

use or in clause:

select count(id) tot  inf_brand_images  is_active=1  ,  ((cmp_brand = '' , brand='$brandname') or (cmp_brand='$id_$brandname') 

possible duplicate:

• mysql query including case or if?